A. Field of Invention
The present invention is related to wireless communication systems, and more particularly, to a method and system of selecting antennas and equipment for use within a wireless communication system.
B. Description of Related Art
In a typical wireless communication system, an area is divided geographically into a number of cell sites, each defined by one or more radiation patterns created by an emission of radio frequency (RF) electromagnetic (EM) waves from a respective base transceiver station (BTS) antenna. For wireless communications, EM signals are not sent through a transmission line, and therefore antennas are required for the transmission and reception of the signals. A group of antennas or an antenna array may be used. An antenna array is a set of antennas working together to produce a particular radiation pattern. Each antenna in the array is referred to as an antenna element (or simply an element).
An antenna can radiate in a specified direction or directions. An antenna produces a radiation pattern, which may either be uniform or non-uniform. A uniform radiation pattern (i.e., omni-directional pattern) may result due to energy radiating from all parts of the antenna and arriving at a distant point at the same time or in phase. As the antenna becomes larger, the radiated energy is distributed in time and does not always arrive at a distant point at the same time. When the energy arrives at different time intervals, the energy does not always add in phase and the result may be a lower amount of received energy resulting in a smaller non-uniform antenna radiation pattern.
An antenna radiation pattern is also referred to as an antenna-beam or beam. A beam width of an antenna is a measure of directivity of an antenna and is usually defined by angles where the radiation pattern reduces to one half of its peak value or more commonly referred to as 3 db points (i.e., 3 decibel power level).
In the typical wireless communication system, each cell site has a BTS, which physically consists of a tower, antennas, and radio equipment. The tower is a large upright structure that provides a frame to mount the antennas. The tower may house multiple antenna systems, and each antenna system may have multiple antenna-elements.
Cell sites are operated by one or more wireless service providers (WSP). A WSP is a company that provides telecommunications through RF signals rather than (or in addition to) through end-to-end wire communication. Each WSP employs a wireless signaling protocol. For example, wireless signaling protocols such as global system for mobile communications (GSM), code division multiple access (CDMA), etc., can be used by WSPs to provide services such as personal communication system (PCS), personal digital cellular (PDC), personal handy phone system (PHS), and others. Communications from a mobile station to a BTS (i.e., reverse link communications) and from a BTS to a mobile station (i.e., forward link communications) are completed using such protocols.
In existing cell sites, each WSP supplies its own antennas and radio equipment. However, multiple wireless service providers may share one tower due to a lack of geographic sites for telecommunication towers and/or to reduce costs. Therefore, a BTS may have multiple groups of radio equipment (i.e., a group of radio equipment may include a receiver, a transmitter, or other equipment) and multiple antennas. Each group of radio equipment may correspond to a separate group of antennas mounted on the tower and to a respective WSP.
When multiple WSPs are served by a single cell site, a large number of antennas and connecting wires (i.e., feeder cables) are required at the cell site to provide air interfaces between mobile stations and radio equipment corresponding to the multiple WSPs, because each WSP needs its own antenna or antennas. In addition, a WSP itself may operate using multiple radio frequencies, and the WSP may require a separate antenna for each radio frequency.
Unfortunately, however, a significant number of towers were originally built to accommodate only a single set of antennas or were imposed with height limitations that have effectively limited the towers to one or two sets of antennas. In addition, many towers have limited space, thus restricting their ability to host multiple antennas, and therefore restricting their ability to host multiple WSPs. Further, installing a large number of antennas is burdensome and costly. Consequently, a system that overcomes these problems is desirable.